You can't. PrestaShop hardcodes all image URLs with .jpg on the end and converts all images to JPGs so that they can be properly resized. It would be very difficult to change this behaviour. It's a feature request that the PrestaShop team are considering for a future PrestaShop version, but it isi unlikely it will make it into v1.4.

You can't. PrestaShop hardcodes all image URLs with .jpg on the end and converts all images to JPGs so that they can be properly resized. It would be very difficult to change this behaviour. It's a feature request that the PrestaShop team are considering for a future PrestaShop version, but it isi unlikely it will make it into v1.4.

What is the purpose of this feature? I assume it is intended to be this way.

Yes, it's by design. Most people don't have animated GIFs as product images. I think it's done so that product images have an appropriate amount of compression, otherwise merchants might upload huge images and then complain that the images take too long to load. Also, the GD library is used to resize images to create thumbnails. I'm not sure how well it handles resizing GIF and PNG images. I doubt it would resize animated GIFs.